The existing liquid crystal display device usually adopts the multi-partitioned dynamic backlight modulation technology to control the brightness of the backlight source. The entire backlight source matrix is divided into at least one partition. The image processing unit extracts the backlight data of the backlight partition according to the grayscale data of the partition image corresponding to the backlight partition, sends the backlight data to the backlight processing unit, and then converts the backlight data into a PWM backlight control signal so as to control the backlight driving part to get command of the brightness of the backlight source in the backlight partition. As such, the portion of the high grayscale image corresponds to a higher brightness of the backlight, and the portion of the low grayscale image corresponds to the lower brightness of the backlight, therefore contrast of light and shade on the screen is improved.